The Structure of Physics
A. Elementary Particle Physics (deals with the tiniest particles known to man)
1. Quantum Electrodynamics (synthesis of quantum mechanics and electromagnetics). Note: the most accurate theory man has ever devised.
2. Quantum Chronodynamics (synthesis of quantum mechanics with the nuclear strong force, the force that holds nuclei together)
3. Electroweak (synthesis of electromagnetism with the nuclear weak force, the force responsible for radioactive decay; works against the strong force.) I believe this theory is also quantized, or sythesized with quantum mechanics.
4. Quantum Field Theory (something of a unification of the previously mentioned theories; not yet a Theory of Everything (ToE))
5. String Theory (highly theoretical attempt to integrate quantum mechanics, and hence all unifications up to date including those mentioned above, with the least understood force of them all: gravity. Of the four fundamental forces, electromagnetic, strong, weak, and gravity, gravity is the least understood. There is no experimental side to string theory, because everything involved is much too small to observe with any existing equipment.) Note on Elementary Particle Physics: you are classified as either theoretical or experimental. You are also classified according to the energies you are working with. High energy, medium energy, low energy are the options.
B. Nuclear Physics (deals with nuclear forces and reactions including radioactive decay)
2. Experiment (includes nuclear engineering)
C. Solid State Physics aka Condensed Matter Physics (the origin of computers is here, along with superconductivity and phases (gas, liquid, solid))
D. Astrophysics (deals mostly with gravity, special and general relativity, and cosmology; also includes astronomy)
E. Optics (classical and quantum theories, wavelets, antennae, lenses, fiber optics, etc.)
F. Mathematical Physics (this really doesn't fit right in with any of the previous categories, but it is extremely important. The term "physicist" wasn't invented until the 1800's; before that, everyone in physics was pretty much what we would now call a mathematical physicist. Also: these people are the theoreticians of the theoreticians. These people, for the most part, do not belong in the lab.)
1. Functional Analysis (deals with abstracting the notion of a function.)
a. Operator Theory
b. Abstract Spaces (metric, normed, Banach, Hilbert spaces)
2. Differential Equations
a. Partial Differential Equations
b. Ordinary Differential Equations
c. Integral Equations and Integro-differential equations
3. Special Functions (Bessel, Laguerre, Legendre, etc.)
4. Algebraic Methods (group theory especially)
Well, I think that's about it for now. I might revise this later.